Enjoy the next few very nice days ahead as major pattern change takes shape…..Undercutting storm track may pick up some badly needed moisture from TS Rosa for good precip producer next week…….

Wednesday September 26, 2018

Posted at 1:26 pm by Howard

9/27/2018 AM Update

Forecast models have come in considerably drier this morning with precipitation for the Tuesday and Wednesday time frame. TS Rosa will not, as of this time, be a player in contributing any additional moisture to the system for the Sierra next week. That closed low approaches the coast Monday, then drops SE along the coast Tuesday and Wednesday. Rosa’s moisture looks destined to affect Northern Baja to AZ, which is more climatically favored for this time of the year. As mentioned below, it is still September and models do not do as great a job in the medium range as they do during the winter. Nevertheless, this mornings guidance still suggest that at least a quarter of an inch of precip is possible and that would translate to a few inches in the high country. This may flip-flop several times in the coming days so back country travelers do not let your guard down….. All in all, it looks like at the least, a good dusting for the high country!

Although High pressure aloft will strengthen the next few days bringing warmer temperatures. The upper high is expected to build north over AK over the weekend as a vigorous belt of westerlies for Late September and Early October undercut and drive into California. With antecedent warmth well established over the Eastern California, there is no doubt that at least moderate to possibly strong winds will develop on Saturday. Pray the Aspens hold on to their leaves this weekend! 🙂

The pattern is complicated as Hurricane Rosa, now gathering strength west of Manzanillo MX, is expected to track NW, west of Baja, CA. Although this storm by the end of the week will be weakening as it moves over colder waters, its moisture is suggested to get somewhat entrained into the southern part of the westerlies. It is not completely known how much of it will get into California at this time, but the models are starting to turn wetter. There is also a cold part of the storm expected to come in Monday night or Tuesday. This would no doubt bring significant snowfall for the backcountry with any additional moisture from Rose.

The principle point here is that anyone planning a trip to the back country, leaving this weekend and traveling next week will need to have their winter gear ready! Snow, Winds Chills, hypothermia are all possible in a snow storm in the high elevations of the backcountry. Some model simulations bring up to a foot in the back country and if more moisture gets involved from Rosa, those amounts would rise. If the opposite occurs, then less snowfall would be expected. The Town of Mammoth will have much lighter amounts. Especially on the roads that are very warm from the Summer. Will update later this week on snow amounts in town if appropriate.

Note:

Going this strong with a forecast of the possibility of snowfall in the backcountry in late September is dicey. Forecast models are not as trustworthy as they would be in December through Mid March timeframe, However, I have to say that as of this time, the Global Models all show snowfall in our back country beginning Monday night and for several days thereafter…..so stay tuned to future developments… For those of you that are headed for the backcountry, you need to keep especially informed…